Membrane adsorbers comprising microporous, flat membranes having chemical moieties capable of binding target substances on their surfaces such as functional groups, ligands, ion-binding sites or other reactants are well known, as is their use for separation of such target substances from liquid feeds. See WO 92 00805 A1. The liquid feed is transported through the membrane adsorber by convective transport.
Typically, membrane adsorbers are used as part of a two-step process of (1) separation of particles by centrifugation or by cross flow filtration and (2) separation of the desired bioactive substance by the membrane adsorber. In an attempt to combine the step of particle separation with separation of the target substance in a single pass through the membrane adsorber, a crossflow filtration process has been suggested using Cibacron blue-modified membrane for the isolation of the enzyme maleate dehydrogenase from E-coli and baker's yeast. 12 Bioforum 455 (1992). According to this process, the particle-laden fluid feed is ridden of cell remnants by directing the feed tangentially across one membrane layer, allowing cell fragments to remain on the membrane's surface while the target substance is collected in the membrane. After removal of the cell fragments by washing the membranes, the target substance is eluted with appropriate solvents. A disadvantage of this process lies in the non-uniform permeation of the target substance through the single membrane layer. This disadvantage can be overcome by the utilization of a spiral-wound cross-flow filtration apparatus as shown in FIG. 10 of U.S. Pat. No. 6,294,090, the pertinent disclosure of which is incorporated herein by reference. However, the process still has an additional drawback in that it requires a large driving force to provide a higher permeate flow and a sufficient overflow velocity for entrainment of the particles with the fluid feed. Otherwise, the first membrane layer would be blinded and the entire permeation process defeated.
Accordingly a primary object of the invention is the provision of a simultaneous separation of particles and target substances from liquid feeds through porous adsorption membranes, characterized by a high adsorption capacity, a substantially uniform flux and by simple construction.